various ‘A’ level geography syllabi. The overlap of material is sufficient for them to offer ‘0’ level meteorology as a kind of bonus to ‘bona fide’ geographers. The physi- cist. however, generally has little or no expertise in climatology, and the physics syllabus is already overcrowded. One agrees with Dr Milford that atmospheric physics should form a compulsory part of any course designed to turn out properly qualified physics teachers, but in practice it is difficult to find more than a few words, usually relating to energy budgets, in any physics syllabus for the Postgraduate Certificate in Education. It is possible that in-service courses and curriculum development might be used for bringing this aspect of physics more generally to the awareness of science teachers. The author had an opportunity to speak to a meeting of science teachers from a West Midlands authority about the new examination. They all expressed inter- est, but none confidence. Only a handful of them were trained physicists. Even the adviser in geography said that teaching meteorology was ‘very low on our list of priorities’.

The feed-back from teachers following the first run-through of the course shows immense enthusiasm, and a general will to overcome or to manage in spite of the difficulties and discouragements mentioned. Many would like to see questions of a type which were more practical or involved more imaginative interpretation of weather maps, but doubtless the examiners will extend the range of questions as opportunity permits.

REFERENCE Milford, J. R. (1980) ‘0-Level’ Meteorology. Weather, 35, pp. 328-329

A CYLINDRICAL CROSS-SECTION ANALYSIS OF THE RAINSTORM OF 8-9 SEPTEMBER 1972 By I. T. LYALL Newark, Nottinghamshire

URING the night of 8-9 September 1972, a heavy rainstorm affected parts of D England and Wales and was most intense in parts of the East Midlands. Totals of precipitation for the 24 hours ending at 0 9 0 0 ~ ~ ~ 9 September 1972 included 60.1 mm at Newton Linford (Leicestershire) and 54.0 mm at Sutton Bonington (Not- tinghamshire) whilst falls of over 40 mm were recorded somewhat more widely. Lyall (1973) noted that the main rain area lay near the track of a rapidly deepening low which moved from near Cornwall at midnight to just off the Yorkshire coast just six hours later, and was due to marked uplift of the very moist air in the warm sector. Most of the rainfall appeared to have occurred in a period of not much more than six hours (probably no longer at any one place).

CYLINDRICAL CROSSSECTION

Since this initial analysis, Pedder (1979) has described a method of analysis based on a vertical cylindrical cross-section, in which it is possible to use the volume described by a cylinder to calculate (from tangential and radial wind components) vorticity, divergence (including net divergence for the volume) and vertical motion.

The present analysis is based on aerological data from ascents made at 2300 GMT on 8 September 1972 and published in the Daily Aerological Record. It has already been shown that the low formed near the right entry of a jet-stream (Lyall 1973) and Fig. 1 shows the surface and 1000-500 mb thickness field at that time. The thickness ridge over the western England Channel indicates the warm sector, with the jet from the south Irish Sea to north-east England also well in evidence.

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Fig. I . Surface pressure (mb. solid lines) and 1000-500 mb thickness (dam, broken lines) ai 0000 G U I on 9 Sepiember I972

Fig. 2. C:ylindrrcal cross-section of temperuture ("C] t'ersus pressure (mb) ui 2300 GMT on 8 September 1972, derived from uscents ai Valeniia, Cbmborne. Crawley, Aughion and Long Kesh

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The thermal structure is shown in Fig. 2 which is a cylindrical cross-section based on data from the stations at Cambome, Crawley, Aughton, Long Kesh and Valentia. The forming low was towards the south-western sector of the cylinder at the time. The atmosphere was baroclinic up to about 600 mb; markedly so in the lowest 300 mb in the south and south-west, delineating the frontal boundaries. At 700 mb temperatures ranged from below -10°C in the west and north-west, where very cold air from the north was being drawn in, to only just below freezing in the warm sector.

Fig. 3 shows analyses of the tangential and radial components of the wind. Posi- tive values of the former indicate cyclonic flow, and of the latter, divergence. In the lower troposphere flow was cyclonic round most of the cylinder, but was still anticyc- lonic in the northern sector; above about 600 mb flow was strongly anticyclonic but to the south it was (rather less strongly) cyclonic, indicative of shear on the flank of the jet stream. The area mean vorticity (not shown) calculated from the average tangential wind around the cylinder indicates a net cyclonic vorticity up to 380 mb.

In the lower troposphere the flow was convergent round most of the circumfer- ence but in the upper troposphere there was a strong flow out of the cylinder in the north and east. Calculating the average radial wind component around the cylinder shows a net convergence in the lower troposphere (Fig. 4), with a level of zero divergence at 550 mb and strong divergence above 450 mb, as would be expected in a developing system.

s-I, (i.e. a divergence of -0.5 X s-I). This seems odd for a developing low and two comments are apposite; (a) a certain degree of coarseness is inevitable in this method which involves interpolation between stations up to 200 km apart; (b) at 300 mb there was a net divergence of 2.8 X s-I, suggesting that an integration up to the tropopause (about 200-250 mb) would yield the more likely positive value for the divergence.

Knowledge of the divergence values permits a calculation of the vertical motion of the atmosphere. This is shown in Fig. 4 and indicates an upward flow which increases

A vertical integration up to 300 mb showed a net convergence of 0.5 X

mb 300

LOO

500

600

700

850

VAL CAM CRAW AUG LK VAL

Fig. 3. Cylindrical cross-section of wind Pow at 2300 GMT on 8 September 1972: (a) tangential to cylinder (continuous lines) and (b) radid to cylinder (broken lines). Positive tangential wind indicates cyclonic pow and positive radial wind indicates divergence

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-8 -6 -4 - 2 2

Fig. 4 . Vertical integration of divergence ( I O - 5 s - L , broken line) and the vertical flow profile (mbhr-', continuous line), averaged over the circular area cut by rhe cylinder, for 2300 GMT on 8 September I972

in the vertical to reach a maximum at the level of zero divergence of 7.65 mbhr-l and then decreases rapidly. Above 380 mb (the level a t which the net circulation becomes cyclonic) the mean vertical wind is downward. It is likely that as the low continued to develop, vertical velocities in the lower troposphere increased, but no further ascent data are available until 1100 on 9 September by which time the system had cleared most of the country.

PRECIPITATION TOTAL

The final stage of this analysis considers the precipitation totals. It is assumed that by about 0 3 0 0 4 0 0 on 9 September, when the storm was at its peak, the value of 7.6 mbhr-' ascent applied to the precipitation-producing levels. Using methods of mass flux as outlined by Wallace and Hobbs (1 977) and assuming (based on the 2300 data) that the lower layers of the warm sector held about 10 gkg-' moisture, the theoretical rainfall in a six hour period over the entire area is 4.6 mm. Maximum falls were actually of the order (as noted) of 40 mm. It would thus seem likely that the main rainfall affected rather more than 10 per cent of the area. The total area covered by the cylinder was about 80 000 square miles, so about 9000 square miles were probably affected. The main rain area was to the right (east) side of the cylinder and must have affected a region somewhat greater than 50 miles wide, which is in good agreement with the observed distribution of rainfall.

Lyall, 1 . T. (1973) A heavy rainfall in the East Midlands. Weather, 28, pp. 289-293 Pedder, M. A. (1979) Vertical cross-section analysis based on a cylindrical projection.

Wallace, J. A. and Hobbs P. M. (1977) Atmospheric science: an introductory survey.

REFERENCES

Weather, 34, pp. 258-265

Academic Press, London

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Photograph by courtesy of The Standard

Phorogroph by courtesy of Daily Express

THUNDERSTORMS OF 6 AUGUST, 1981 These are just two of the many spectacular photographs which made front page news in the

morning papers after the severe storms of 6 Au st this year. The organised storms, described as the worst for five years, followed the hottest spefof the summer thus far and affected a large part of England and Wales stretchin from Merseyside to the South and South-East.

Overnight on 5/6 August, &anChester recorded 3.78 in.. its heaviest 12-hour rainfall since records began in 1877. Two severe storms moved across the South-East during the morning. The very great vertical extent of the cloud reduced daylight so much that automatic street lighting came on during both storms. conditions being reminiscent of late afternoon in Novembtr rather than a summer morning. Torrential rain was accompanied b thunder and lightning of unusually fre uent and vivid form. Well over two inches of rain fell in !!urn and Sussex during the storms; the%ndon Weather Centre recorded 1-78 in. between 9 am and % pm. Flooding was widespread in these areas. The thundery activity conhnued to move east during the afternoon but most of the heavier rain died out before reaching the coast.

The associated low pressure system which, in conjunction with a southeastward moving cold front, ave rise to the storms bea'me slow-moving to the southeast of England. No sunshine was recorckd in London and south-eastern counties for three, and in some laces four, days, the Ion est period without sunshine in August for at least 20 ears. Some Rrther, locally heavy, outkealts of rain accurnd in central areas during this period:

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